This invention relates to transreflectors that reflect a greater portion of the light that strikes one side of the transreflectors and transmit a greater portion of the light that strikes the other side of the transreflectors or vice versa. Also, this invention relates to different methods of making transreflectors.
A transreflector is an optical device that transmits part of the light that strikes it and reflects part of the light that strikes it. An example of a transreflector is a beam splitter or half-silvered mirror. Consider the light intensity that strikes a given side of a transreflector, by conservation of energy, the sum of the light intensity that is (i) transmitted through the transreflector, (ii) reflected by the transreflector and (iii) absorbed by the transreflector must equal the original intensity striking that side. If one desires to construct a transreflector that transmits as much of the light striking one side of the device as possible while also reflecting as much of the light striking the opposite side of the device as possible, a beam splitter type transreflector device is theoretically limited to 50% light transmission and 50% light reflection assuming that the intensity of the light absorbed by the device is zero. Since it is not physically possible to create a transreflective device that has zero light absorption, a beam splitter type transreflector device that attempts to both transmit and reflect the maximum amount of light incident on the device will be limited to less than 50% transmission and less than 50% reflection.
Transreflectors may be used, for example, with liquid crystal displays (LCDs), used in laptop computers, personal digital assistant devices (PDA), word processors, avionic displays, cell phones and the like to permit the displays to be illuminated in dark environments by a backlight and in lighted environments by ambient light without the need to power the backlight. This is done, for example, by placing the transreflector between the backlight and the LCD. In lighted environments a portion of the ambient light passes through the display and a portion of this light is then reflected by the transreflector back through the LCD to illuminate the display. In dark environments, a portion of the light from the backlight is transmitted through the transreflector and through the LCD to illuminate the display.
In order to make the display as bright as possible in both lighted and dark environments, the ideal transreflector would transmit 100% of the light from the backlight striking it from below and reflect 100% of the ambient light striking it from above. Optical losses in the transreflective device, absorption for example, make it impossible to obtain 100% transmittance of light striking the transreflector from below and 100% reflection of light striking the transreflector from above. However, it is desirable to be as close to 100% transmittance and 100% reflection as practically possible.
Beam splitter type transreflectors treat light striking the top surface from above and light striking the bottom surface from below the same, and are limited to less than 50% for both transmission and reflection of light striking a surface of these devices. Therefore, beam splitter type transreflective devices are limited to transmitting less than 50% of the light from the backlight striking them from below and reflecting less than 50% of the ambient light striking them from above, which falls far short of the ideal 100% transmission from below and 100% reflectance from above needed to make a display as bright as possible.
In order to make displays as bright as possible, there is a need for transreflective devices which treat light striking them from above differently than light striking them from below. In addition these transreflectors should transmit as much of the light that strikes them from below as possible (e.g., greater than 50%), and reflect as much of the light that strikes them from above as possible (e.g., greater than 50%).
The present invention relates to transreflectors, transreflector systems and displays and methods of making transreflectors that reflect more of the light that strikes one side of the transreflectors and transmit more of the light that strikes the opposite side of the transreflectors.
In one form of the invention, the transreflector comprises a transparent substrate (which may be a film or plate) having a pattern of optical deformities possessing reflective and non-reflective light transmissive surfaces on or in one side of the substrate. The term xe2x80x9ctransparentxe2x80x9d as used throughout the specification and claims means optically transparent or optically translucent. The transreflector may also comprise two or more substrate/film layers that have been bonded together with the optical deformities on outer surfaces of the outermost layers. These optical deformities may comprise grooves or individual optical deformities of well defined shape. Also, the size, height, shape, position, angle, density, and/or orientation of the optical deformities may vary across the substrate. The reflective surfaces are coated with a reflective coating that may comprise a polarization coating. The transmissive surfaces may be textured, lensed or have optical shapes to redirect light, and may also have an optical coating such as an antireflective or polarization coating. The pattern of reflective and non-reflective light transmissive surfaces may be on the top side of the substrate (i.e., the surface nearest the LCD) or the bottom side of the substrate (i.e., the surface nearest the backlight). The reflective and transmissive surfaces may vary in size, shape, angle, density and orientation.
In the case where the pattern of reflective and non-reflective surfaces are on the top side of the transreflector, the other side or bottom of the transreflector may either be planar or have optical shapes designed to better transmit a certain distribution of light, for example the output distribution of a backlight, and may in addition direct this light to the light transmissive surfaces. These optical deformities may comprise grooves or individual optical deformities of well defined shape. Also, the size, height, shape, position, angle, density, and/or orientation of the optical deformities may vary across the transreflector. An optical coating such as an antireflective or polarization coating may also be applied to the bottom of the transreflector in addition to or in place of the optical deformities.
In the case where the pattern of reflective and non-reflective surfaces are on the bottom side of the transreflector, the other side or top of the transreflector may either be planar or have optical deformities to redirect light. For example, the top side of the transreflector may have optical shapes which redirect light transmitted through the transreflector more toward the normal direction of the LCD so that more light from the transreflector is transmitted through the LCD. These optical deformities may comprise grooves including but not limited to prismatic or lenticular grooves, or individual optical deformities of well defined shape. Also, the size, shape, angle, density, and orientation of the optical deformities may vary across the transreflector. The top surface of the transreflector may also be textured or have an optical coating such as an antireflective or polarization coating.
Such a transreflector may be made by applying a reflective coating to one side of a transparent substrate and then thermoforming such one side to provide a plurality of spaced angled reflective coated surfaces and a plurality of angled non-coated light transmissive surfaces. The angles of both the reflective and non-reflective light transmissive surfaces may be chosen to optimize performance. Also, optical deformities may be formed on the other side of the substrate.
Alternatively, such a transreflector may be made by thermoforming one side of a transparent substrate to produce a plurality of spaced angled surfaces and a plurality of other angled surfaces, and then applying a reflective coating on the angled surfaces to make them reflective surfaces while leaving the other angled surfaces uncoated. This can be accomplished, for example, by depositing a reflective coating onto the angled surfaces but not onto the other angled surfaces using a line of site or other appropriate deposition technique.
In another form of the invention, the transreflector comprises two or more transparent substrates of different indices of refraction bonded together along mating sides of the substrates. The mating side of at least one of the substrates has a pattern of optical deformities and the mating side of the other substrate has an inverse pattern of the optical deformities on the mating side of the one substrate. The other side of the substrate that has the lower index of refraction may be planar or have optical deformities designed to accept a specific distribution of light emitted from a backlight or other light source. The other side of the substrate with the higher index of refraction may be textured or have optical shapes to redirect light entering or exiting the transreflector from this surface. The other side of either substrate may also have an optical coating applied such as an antireflective or polarization coating. An optical coating may also be applied to either of the mating surfaces before the two substrates are bonded together, resulting in an optical film at the mating interface of the two substrates after the two substrates are bonded together.
Such a transreflector may be made by preforming a pattern of optical deformities on or in one side of the two transparent substrates of different indices of refraction and using the preformed pattern of optical deformities of the one substrate to form an inverse pattern of the optical deformities in or on one side of the other substrate by melting or heat softening one side of the other substrate and pressing the melted or softened side of the other substrate against the preformed pattern of deformities on or in one side of the one substrate to form the inverse pattern on or in the one side of the other substrate while preventing such one side of the one substrate from melting. Both of the substrates are then cooled to cause the one side of the other substrate to solidify and bond with the one side of the one substrate. Also, optical deformities may be formed on or in the other side of either of the substrates either before, after or during bonding of the two substrates together.
Any of these transreflectors may be used in a transreflector system or display to transmit light emitted by a backlight or other light source incident on one side of the transreflectors and for reflecting ambient light incident on the opposite side of the transreflectors. The side of the transreflectors that receives incident light from a backlight or other light source may have optical deformities designed to better transmit a particular output distribution of the light emitted from the light source, and may include an angular shape pattern that changes with the distance from the input edge of a backlight to compensate for changes in the angular distribution of the light emitted from the backlight as the distance from the input edge of the backlight increases. The optical deformities on the side of the transreflectors that receive light from the backlight or other light source may comprise grooves or individual optical deformities of well defined shape. Also, the size, shape, angle, density, and orientation of the optical deformities may vary across the transreflectors.
The other side of the transreflectors which receives incident ambient light may be textured or have optical shapes to redirect light entering or exiting the transreflectors from this surface. The optical shapes on the side of the transreflectors that receive ambient light may comprise grooves or individual optical deformities of well defined shape. Also, the size, shape, angle, density, and orientation of the optical deformities may vary across the transreflectors. An optical coating such as an antireflective or polarization coating may also be applied to either surface of the transreflectors in addition to or in place of the optical deformities.
Likewise, the backlight may have a pattern of individual optical deformities for producing a particular light output distribution from its light emitting surface that have a well defined shape including at least one sloping surface for reflecting or refracting light impinging on the optical deformities out of the light emitting surface. The sloping surface of at least some of these deformities may be oriented to face an optically coupled area of the light input edge across the backlight. Also, at least some of the deformities, which may comprise depressions in or projections on the light emitting portion of the backlight/panel member, may vary in size, shape, depth or height, density and/or orientation across the backlight. Moreover, the deformities may be randomized, staggered, or arranged in a stochastic pattern across the backlight. Further, at least some of the deformities may be arranged in clusters across the backlight, with at least some of the deformities in each of the clusters having a different size or shape characteristic that collectively produce an average size or shape characteristic for each of the clusters that varies across the backlight. This allows the light output distribution of the backlight and the light input surfaces on the transreflectors that receive incident light from the backlight to be tuned to each other so that the transreflectors will better transmit more of the light emitted by the backlight. Also the side of the backlight closest to the transreflector may have optical deformities which align with the deformities on or in the transreflector to increase the efficiency with which light is transmitted from the backlight to the transreflector. The region between the aligned backlight and transreflector deformities may contain a refraction index matching material to further increase efficiency. A display may be placed in close proximity to the side of the transreflectors facing away from the backlight.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter more fully described and particularly pointed out in the claims, the following description and annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but several of the various ways in which the principles of the invention may be employed.